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Risk of Autism Higher in Younger Siblings

August 16, 2011

(Ivanhoe Newswire) — The risk that an infant with an older sibling with autism will also develop the disorder, previously estimated at between 3 and 10 percent, is substantially higher at approximately 19 percent, according to this study. While the study found a combined estimated risk for all participants of nearly19 percent, it found an even more elevated risk of recurrence of over 26 percent for male infants, and over 32 percent for infants with more than one older sibling with autism.

The study is the largest prospective investigation of autism spectrum disorder and sibling recurrence to date.

The study has important implications both for genetic counseling for parents and for referral to early intervention for the infant siblings of children with autism if concerns arise about their development, said Sally Ozonoff, professor of psychiatry and behavioral sciences at the MIND Institute and the study’s lead author.

Autism is a complex disorder that affects a child’s ability to think, communicate, interact socially and learn. The U.S. Centers for Disease Control and Prevention places the incidence of autism at 1 in 110 children born today.

The participants in the study were enrolled in separate studies that are part of the Baby Siblings Research Consortium, an international network supported by Autism Speaks. There is strong evidence that genetic factors play a critical role in vulnerability for developing autism.

The study subjects were tested using the Autism Diagnostic Observation Schedule (ADOS), an autism diagnostic tool, and the Mullen Scales of Early Learning, which measures nonverbal cognitive, language and motor skills. Of the 664 participants, a total of 132 infants met the criteria for an autism spectrum disorder. Fifty-four received a diagnosis of autistic disorder and 78 received a diagnosis of Pervasive Developmental Delay Not Otherwise Specified, considered a milder form of autism.

More males than females are affected with autism “” 80 percent of all affected children are male. The risk to male children held true in the current study. The overall rate of autism spectrum outcomes for all study participants was 18.7 percent. However, there was a significant difference in the recurrence rate based on whether the child had one sibling or more than one sibling with autism. In families with one older child with autism, or simplex families, the rate of incidence was 20.1 percent. Only 37 of the study participants had more than one sibling with autism. But for those families, called multiplex families, the recurrence rate was 32.2 percent.

“It’s important to recognize that these are estimates that are averaged across all of the families. So, for some families, the risk will be greater than 18 percent, and for other families it would be less than 18 percent. At the present time, unfortunately, we do not know how to estimate an individual family’s actual risk,” Ozonoff was quoted as saying.

“Parents often ask what their risk of having another child with ASD is and, until now, we were really not sure of the answer,” Ozonoff said.

The study also highlights the critical importance of routine surveillance and rapid referral for treatment of infant siblings of children with autism. Ozonoff said that it is of paramount importance that primary care professionals monitor these children’s development closely and refer them for early intervention immediately when concerns arise.

SOURCE: Pediatrics, published online August 14, 2011




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